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THE STOMACH                                   347

them—are literally double teeth* This Is a suggestion, of the
more complicated teeth of the Zeuglodonts, and shows so far
tiiat the simple conical teeth of existing Whales 'cf. however the
Platanistidae) are not by any ihanrier of means so primitive as
their actual structure would undoubtedly lead one to lj»elieve.
Further than this, the greater number of teeth in the older
embryo coincided with the disappearance  of  these  double  teeth*
which seem to split up into the simple conical teeth.
The Toothed Whales are not furnished with  baleen, but with
teeth only* These teeth are more or less numerous, their
arrangement being of value in the classification of the group;
a matter which is dealfe with later.
In  the  Narwhal, whose  dentition in the adult  is reduced to
the well-known tusk or tasks (properly developed only in the
male), there is a complete foetal dentition. A very curious fact
lias been, elucidated by Professor Kukenthal alout the dentition
of the Common Porpoise.      It appears that In this Cetacean the
two teetli corresponding to each other of the two dentitions may
fuse into a single tooth, which has in consequence a double crown.
It may be tfaafe this is the case with the Platanistid Inia, and
that its diconodonfc teeth are not, therefore, a reminiscence of tiie
comparatively complicated teeth of the ancient Zeuglodonts.
The internal organs of Whales which show the greatest
peculiarities as compared with other mammals are the stomach,
the lungs, and the diaphragm. Whales always possess a com-
plicated stomach divided into many, but into a variable number
of, chambers: there are as few as four in some, as many as fourteen
in Ziphioids.
On account of its complication the stomachl lias been
compared to that of Ruminants—it has eyen been alleged that
Whales " ruminate "—but the comparison will not hold good.
NOT, on the other hand, is there a -very close resemblance to the
equally-complicated stomach of the Sireniana
The Rorqual has a stomach with as few compartments as any.
The only "Whale which appears to have fewer is JSalaena vnysticefas,
where there are but three* In the Rorqual the oesophagus opens
into a more or less globular sac; from the upper end of this,
t,e. close to the entry of the oesophagus, arises the second chamber*
long and narrowish; then follows an extremely short third
* For details and literature see Jiw&klaiLS* Jfeft* ZeitscJi-r. xxni. 1S9S, p. 1*